Although it is not widely known, among the pharmacological properties of nicotine is the ability to cause a reduction in lung concentration of a key metabolic intermediate, S-adenosylmethionine (AdoMet). This metabolite plays important roles in gene and enzyme regulation, polyamine biosynthesis, methionine cycling and folate metabolism. The fungus Pneumocystis, an important lung pathogen for immunosuppressed persons which causes Pneumocystis pneumonia (PCP), requires AdoMet, as do all other cells. However, Pneumocystis is unique in being able to synthesize this compound itself and must obtain AdoMet from its host. We have data showing that nicotine treats PCP in a rat model. Supporting this are clinical data from a large study of AIDS patients showing that PCP relapse is less frequent among smokers. The following Aims will be pursued: Aim 1. We will study the ability of nicotine to treat rat model of PCP: We will look for synergism using nicotine and trimethoprim/sulfamethoxazole, the primary drug for treatment of PCP. Both the epimer S-(-) produced by plants and the R-(+) epimer produced in tobacco smoke will be examined. Aim 2. We will study the tissue specificity of the effect of nicotine isomers on AdoMet. We hypothesize that the effectiveness of nicotine in treating PCP relates to the selective effect of nicotine on lung AdoMet. We will examine various animal tissues for nicotine-induced changes in the intracellular AdoMet pool. Aim 3. We will study the mechanism by which nicotine isomers induced AdoMet depletion in the lung. The mechanism underlying nicotine-induced AdoMet depletion in lung tissue could be a decrease in AdoMet synthesis, an increase in polyamine metabolism, an increase in methylase activity or a combination of these. We hypothesize that increased polyamine metabolism is most important but will examine all three potential mechanisms. Aim 4 We will study differential protein expression in lungs of rats chronically treated with nicotine. Although we can describe the logical mechanisms by which nicotine could affect AdoMet, it is possible that unanticipated mechanisms could be involved. Completion of these Aims will lay the groundwork for developing the nicotine or nicotine analogues as sole or adjunctive therapy for PCP.